ok the car is a 91 si crx.. with an 11 inch fast brake kit.. its using integra calipers front and rear new stainless steel lines... car has great brake pressure when not running when running it goes right down to the floor .... i have bled the brakes many times swapped out the civic ex master cylinder and brake booster with a new type r 1 inch master cylinder and booster and still the same problem i orginally thought it would of been the booster but now on the second one with the same issue.. any thoughts??

 

Have you checked the hard steel lines that run to the rear. They could be worn out.

 

they look good.. no leaks anywhere.. the one thing i didnt do was bench bleed the master cylinder so going to try that and see where it goes